What is a meta-analysis?
A meta-analysis is a two-stage process. The first stage is the extraction of data from each individual study and the calculation of a result for that study (the 'point estimate' or 'summary statistic'), with an estimate of the chance variation we would expect with studies like that (the 'confidence interval').
The second stage involves deciding whether it is appropriate to calculate a pooled average result across studies and, if so, calculating and presenting such a result. Part of this process is to give greater weight to the results from studies which give us more information, because these are likely to be closer to the truth we are trying to estimate. We'll come back to these topics in later modules.
The results of meta-analyses are often presented in a forest plot. Run through this PDF file, which explains the parts of these plots.